Antarctica is the world’s great cooling unit. This vital part of Earth’s climate system is largely powered by the annual freeze and melt of millions of square kilometres of sea ice around the continent.

Our research shows changes to this annual freeze cycle in McMurdo Sound can lead to shifts in the diversity of algal communities that live within the sea ice.

At the start of the southern winter, as sea water begins to freeze, it expels salt and forms heavy and very cold brine. This sinks to the seafloor, ultimately forming what’s known as Antarctic Bottom Water. This is then pumped out to the rest of the world through several major oceanic currents.

Historically, this cycle meant that Antarctica effectively doubled in size and the continent was surrounded by an enormous apron of sea ice at the peak of winter. But the changing climate is shifting this annual cycle.

For the past decade, Antarctic sea ice has been in decline. It hasn’t been a steady trend, but each year since 2016 less sea ice has formed compared to historic averages.

Antarctica’s annual maximum sea ice extent in September 2023 was the lowest on record, with approximately 1.75 million square kilometres less sea ice than normal – an area equivalent to about 6.5 times the land area of........

© The Conversation